1. Field of the Invention
This invention relates to the separation of greases and oils from water using automatic processes and apparatus.
2. Description of Related Art
Grease separators are used to separate and remove for recycling the grease, oil and dirt found in wastewater which has been used in food preparation establishments. The primary source of such wastewater is water used to clean stoves and grills and from dishwashers, with mop water and floor drains a secondary source. The wastewater may contain fats, oils, greases, soap residues, dirt, and floor sweepings. Grease, oil, fats, and other materials found in wastewater which have a density less than that of water will be referred to collectively in this application as "light fluids" or as "grease and oil".
There is a problem with the disposal of such wastewater in sewers because of the tendency of grease to coagulate on the internal walls of pipes and plug the lumen of the pipes, a particular problem at bends and valves. In addition, many jurisdictions charge a fee for the disposal of wastes having a high biological oxygen demand, such as food establishment wastewaters. Finally, the salvage value of grease and oil recovered from wastewaters provides an additional economic incentive for separation and recovery of the grease and oil.
Grease separators generally include a tank in which the wastewater stream is allowed to stand while the grease and oil separate. The grease and oil accumulate at the top of the tank because grease and oil is less dense than is water. Automated separators have provisions for heating the fluids to prevent coagulation of the grease and oil and have means for detecting the grease and oil level to allow for the automatic removal of grease and oil when the separator approaches its capacity. Conventional systems have sensors to detect the level of grease and oil. These sensors are inactivated or severely inhibited in their response when coated with grease and dirt, necessitating frequent cleaning to maintain operation of the separator. In addition, conventional systems use electrical resistance heaters to maintain the grease and oil in liquid form for removal. Such heaters present safety problems and are expensive to operate.
U.S. Pat. No. 2,253,711 discloses a system for separating ballast water and oil in sea-going vessels. A capacitance probe is used to continuously measure the dielectric constant of the fluids in the system in order the detect the presence of a slug of oil.
U.S. Pat. No. 4,543,191 discloses the use of a capacitance cell used to measure the capacitance of an oil stream in the presence of basic sediment and water.
U.S. Pat. No. 4,820,425 discloses a robotic filtration station in which capacitance measurements are taken to determine the conclusion of the filtering process.
U.S. Pat. No. 4,880,533 discloses a grease separator having sensors which operate by determining the heat transfer rate of the medium in which the sensor is immersed. A microprocessor responds to changes in the heat transfer rate by activating a grease skimmer and valves.
U.S. Pat. No. 5,400,651 discloses an apparatus which uses spaced capacitance probes to determine the presence of water in an oil storage tank.
U.S. Pat. No. 5,431,826 discloses an automatic grease separator in which electrodes which measure conductivity of the medium are used to determine the level of grease in the separator and to activate a valve which allows the removal of grease. A electrical resistance heater is used to maintain the grease in the fluid state.
Capacitance probes have the desirable characteristic of insensitivity to coating with the grease, oil and dirt often found in wastewater. Their use in the grease separator of this invention fulfills a long felt need for a reliable grease separator which does not require frequent cleaning. In addition, the current invention avoids the problems of electrical heaters in the separator by using heated make-up water to maintain fluidity of the grease and oil before removal.